1. Field of the Invention
The present invention relates to an attachment attached detachably to a main spindle of a machine tool.
2. Description of Related Art
A machine tool for machining is designed to perform various cutting processes with various types of tools attached normally to the nose of its own main spindle depending on the necessity. Furthermore, a machine tool is designed to perform cutting processes on workpieces in a direction different from the direction in which the axis of its main spindle extends by attaching an attachment to the nose of its main spindle additionally. The attachment has an attachment main spindle which is arranged in a direction which crosses over the axis of the main spindle of the machine tool. A variety of tools are detachably attached to the nose of the attachment main spindle. When the attachment is attached to the main spindle of the machine tool, the attachment main spindle is revolvably driven in linkage with the main spindle of the machine tool, and thereby the machine tool performs a cutting process.
By attaching an attachment to the main spindle of the machine tool in the foregoing manner, the direction of the attached tool can be changed. Accordingly, the machine tool is capable of performing a wider range of cutting processes and of performing a cutting process on a workpiece which can hardly be processed by a tool attached normally to the machine tool's own main spindle.
In addition, when an attachment is attached to the main spindle of the machine tool, the appropriate one is selected from various attachments such as a right-angle head, a universal head (Japanese Patent No. 2731992, Japanese Patent No. 3407900, and Japanese Utility Model No. 2556950) or the like, in view of the shape of the workpiece, a direction in which the process surface of the workpiece extends, restrictions the cutting edge diameter of the tool which is going to be used, and the like.
An attachment such as a right-angle head or a universal head makes it possible to index the attached tool in the horizontal plane by swiveling itself about a vertical shaft. Furthermore, an attachment such as a universal head is one to which a tool is attached revolvably in multiple directions, for allowing greater flexibility in processing position of the attached tool than an attachment such as a right-angle head. In other words, the attachment such as a universal head makes it possible to index the attached tool in the vertical plane by swiveling its attachment main spindle about a horizontal shaft.
However, in the case of an attachment such as a universal head, when the attachment main spindle switches from a revolving state to a state of swiveling in the vertical plane, the gear coupling in the indexing mechanism disengages. This causes a condition in which the attachment main spindle does not mesh with any gear at all (a neutral condition) until the gear of the horizontal shaft meshes with an indexing gear. As a result, it is likely that the tool attached to the horizontal shaft with the attachment main spindle interposed in between may swivel in the vertical plane in an unintentional direction due to its own weight and cause a wrong indexing.